As a rubber composition for an automobile tire, a rubber composition containing a conjugated diene-based polymer such as polybutadiene or a butadiene-styrene copolymer and a reinforcing agent is used.
In recent years, with increased concern about an environmental problem, requirements of fuel cost-saving properties on an automobile have been increasing, and a rubber composition used in a tire for an automobile has also been required to be excellent in fuel cost-saving properties.
For example, as a polymer which enhances fuel cost-saving properties and a polymer composition favorable in fuel cost-saving properties, JP-A 7-82422 has proposed a polymer obtained by living anion polymerization of butadiene, styrene, and dimethylaminomethylstyrene using alkyllithium as a polymerization initiator, and a polymer composition containing the polymer and carbon black. JP-A 1-217011 has proposed a conjugated diene-based polymer in which one end of a polymer obtained by copolymerization of butadiene and styrene using alkyllithium as a polymerization initiator is modified with bis(dimethylamino)methylvinylsilane, and a polymer composition of the polymer and carbon black.